Combined noise suppresser and tuning indicator



Im@ 23, w36. D w. R. KOCH l 2,045,542

i l COMBINED NOISE SUPPRES SER AND TUNING INDICATOR Filed Aug. 5, 193370 55m/rm WINFIELD R. KOCH BY I I f u r a ATTORNEY fioV Patented June23, 1936 D NOISE sUrPnnssER TUNING INDICATOR Winfield It, Koen, Camden,`=N. J., assigner to Radio Corporation of America, a corporation 'Y ofDelaware Atplitation August 193s, serialNe. teas'sfl 1o claims.(elast-azul My 4present invention vrelates' to 'radio receiver controlcircuits, and more particularly to 'a com bined Yback-ground noisesuppresser and tuning indicator for a radio receiver.

- Ther-'e are certain types l'of 'radio receiving systems wherein it isdesired to have the receiver renderedinoperative to reproduce electricalimpulses impressed thereon until 'a predetermined signal intensity levelhas been attained. vvFor ex*- 'anlple, radio receivers lincludingautomatic 'volume control, or receivers of the automatically tuned type,are illustrations of such -types of receivers. In the case of the'former when the 'received signal intensity -talls below a predeterminedintensity level, the action Yof the automatic volume control is Vin adirection such that background noise impulse'sare lg-rez'ttly'annlliiied-V y Y In the case of receivers utili-zing automatic tuning,the automatic tuningl mechanism'tends to produce undesired electricalimpulses which arereproduced when the system is tuned from onepredetern'lined station position t'o another one.,` It is highlydesirable to silence, or quiet, the receiving system between such`pred'et'e'rn'lilre'd tuning points. There may fbe other Situationswhere it is desired to rend'er the receiving system inefficient wheneverthe useful signal energy =de creases below a predetermined point'.'

Accordingly, it maybe stated that lit is one of the main objects of mypresent invent-lento 'previde a Acombined background noise fsuppresservand tuning aid whereby the receiving system will be rendered silentexcept Vwhen a signal is tuned in, the suppresser also functioning as atuning indicator when the desired signal energy exceeds a predeterminedintensity level.

Another important object of the vpresent ineneon glow tube between thedetector yand the audio Yfrequency networkfof a radio receiver, the

glow' tube not only functioning as an inc'l'icatorY to show when signalenergy above a Vpredetermined intensity level has been received, .but.additionally acting to maintain the transmission eiciency between thedetector n and network relatively low until said intensity l'evelha'sbeen exceeded. l y

-Still other objects of fthe present invention fare to improvevgener-ally the simplicity fand eieieney not only reliable in operation,`but 'economically manufactured 'andassembled in a radio receiver.

iThe novel yfeat'l'nes Which'ibel'ieve to be chaiacteristic of myinvention are set vforth in par'- ticularit'y in 'the -'amoend'edclaims, the inv'entien itself, however, Vas to :both itsAorganizat'i-'o'n and method df ep'eration `will best be understood IcylreT-eren'cfe to ltlle follo'v'ing description taken in connection 'withthe A"l'rjaw'ing 'ln which I -have indicated diagrammatically severalarrangements for carrying my invention into effect. I In the'dra'wing',Y

Figi l fdi-agrarnmatically 'shows la receiver e'mbodying one for-rn ofthe present invention,

Figs. 2 and 3 respectively show two different modi-'ncation'softhe'-'inv'er'l't-,ion. l

Referring new toene accompanying drawing wherein like referencecharacters in tne'dlnerent ng-urjes designate similar c'lrcultelement's,there is shown in Fig. y1 'a lr'eceilling system 'of a well known type.For this 'reason the receivin'gs'y's'ftem circuits `are ystron-n inVvpurely conventional form, those skilled fin Vthe Aart being 'wellaware of the details 'not specifically shown in the drawing. ForVexample, 'the receiving system embodies the usual signal energycollecting means, such fas' a grounded antenna System n, the antennabeing coupled fte'fa network' f1 through a tunable signal selector 2. Itxavi-l1 be nnder'stoodfthat fthe net-7 work I represents one or morefstages fof tuned rad-lo '-rreq'uency amplifcatlon arranged 'li-ncascade, `:and Ythat the inlunleral A3 designates the tuni g means for'such stage,V or 'sta-ges. v

"numeral -`3 des'igl'late's the symbolic representati'en Yef thevariable 4tuning condens'erine'ans of the radio ifre'quency 'amplifiernetwork.; The, output "of 'the netwerk "I, -i's impressed, vasfat M1',upon 'the 'li'llllable inpt circuiti o'f the detector stage, which:stage includes electron discharge tube `5. 'The tuning circuit-,ilincludes a tuning cb'rlliilSer 6, and 'the r'rzeiitfol g'ri'd-oathed'eOil'- cuit of the detector tube 5 includes the usual leaky grlidcondenser cn'structi'n. -o'r detecting by grid rectmeation. v n I enaudlo '-,frequency ampliner stage succeeds the detector 'tube 5, thecontrol ygrid 'of the audio amnlier 'tube fleeing-*connected to 'theanode 'of the gaseous glow -'tute il, the latter being er theY neon gastype. .Positive potential iis supplied to which includes the lead 9connected to the positive side of the source B. This source is notshown, but it may be an alternating current source, whose output isproperly rectified and filtered; or it may be a direct current source.The negative side of the source B is represented by the groundconnection of the cathode leads of tubes 5 and 1. g y

The anode of tube.5 is connected tothe positive potential supply lead 9through a resistor I0, an intermediate point of said resistor beingconnected to ground through a by-pass condenser I I in order to by-passradio frequencies. One terminal of the neon glow tube 8 is connected tothe anode side of plate circuit filter resistor I0, while the otherterminal is connected to ground through resistor I 2, a condenser I3being connected between ground and an intermediate point of re-`v sistorI2. The anode of tube 'I, and the lead 9, may be connected to anotherstage of audio frequency amplication, or, as shown in the draw-I As faras the operation of the combined noise` suppresser and tuning indicatoris concerned, the

` networks preceding the detector tube 5 maybe of any desired type. Inother words, it makes little difference whether the network I embodiesthe usual superheterodyne receiver `stages ahead of the second detector,or whether the network ahead of the detector tube 5 is a cascadedtunedradio frequency amplifier network. Where the receiver is of thesuperheterodyne type the condenser Bis, of course, fixed, and resonatesthe circuit 4 to the operating intermediate frequency,`

the numeral 3 in that case designating the tuning meansrfor the signalandn local oscillator cir- 'cuits feeding-the .intermediate frequencyamplifier supplying the second detector tube 5. Ifv the receiver is ofthe tuned radio frequency type, then the numeral 3 is to be understoodas designating the tuning means for the cascaded tunable radio frequencyamplifiers, and is to be considered as adapted for uni-control with ,thelvariable condenser 6.

The operation of the tube 8 and itsassociated circuits will Vnow beconsidered in order to show how its operation adapts it for use withreceivers of various types as discussed heretofore. Assuming that thetuning means of the receiver has been adjusted to a certain station, letit be further assumed that the tuning means is desired to be adjusted toa different station setting, As the receiver is tuned away from the oldsetting, the

signal energy intensity level, considered with re- Since the strikingvoltage .of the neon glow` tube 8 depends upon the detector platevoltage, it

will be seen that with no signal input to thedetector the neon `tubeisbelow its striking voltage,`

and Ait does not glowortransmit energy.VV The bias resistors are R1 andR2, and they function to keep the cathode of audio tube 'I at asubstantial positive :potential with:` respect to the ,-B

side of thesystemf The grid is at f-B potential,`

and the tube 'I is, accordingly, biased beyond cutoif until the neontube 8 begins to function. When signals are received, that is when thetuning means of the receiver is adjusted to the new station setting, thedetector plate voltage rises. 5 The striking voltage of the tube 8 isexceeded, and the neon tube glows. The current through the neon tubereduces the negative bias on the control grid of tube 'I to a point suchthat the audio amplifier tube is rendered operative. Si- 10.multaneously the neon tube also transfers audio signal energy from thedetector plate circuit to the lcontrol'gri'd circuit ofthe audio tube.

It will now be seen that when a signal is tuned `in andthe detectorplate voltage rises, the neon 15 Vtube-breaks down, and by its glow actsas an indicator to inform the operator that a station has beentuned in.vIt will also. be observed that the tube 8 not only functions to renderthe audio tube operative or inoperative, but, in addition, functions asa coupling device to transfer audio signal energy from the detectorcircuit to the audio network. TheV resistor I2 and condenser I3 are sochosen as to give the proper time delay constant to preventbursts ofstatic from operating the 25 .tube 8- The combined suppresser and tuningindicator of the present invention is shown adapted to a receivingsystem utilizing an automatic volume controlarrangement in Fig. l. Theautomatic 30 Volume control arrangement is of `a purely conventionaltype and embodies a diode rectifier havin-g its cathode connected to thehigh potential side of Vcircuit 4 and its anode connected throughresistor I5 to the low potential side of the detector 35. input circuit.The usual conductive connection I6, including the resistor-capacityfilter II, II, is connectedbetween the point of negative potential onresistor I5 and the grid circuits'of networkl I. u Those skilled in theart are well aware of therspecific circuit connections of anvautomaticvolume Vcontrol arrangement, and how the gain control leadfrom thecontrol rectifier is to be connected to the grid circuits of thecontrolled amplifiers, The action of the automatic volume controlarrangement may be improved by operating the diode rectifier from abroad circuit, leaving the detector working from a sharp circuit. Thenoise suppresserwould then operate over a narrower band..

AIn a system employing automatic volume control the present invention isparticularly useful, since, if the signal energy amplitude decreasesbelowa predetermined intensity level, the tube 8 promptly renders theaudio amplifier inoperative, and, additionally, ceases to transfer audioenergy fromv the detectorA circuit to the audio network.. The tubeitself, due to its failure to glow, informs'the operator that while thereceiver is tuned to the proper station setting no signal energy is'actually being impressed across the detector input circuit 4.

Similarly, in the case of a receiver including automatic tuning for thevariableV condensers 3 65 and 6,; thedevice 8 and its associatedcircuitsV Y function to prevent audio reproduction between predeterminedstation settings. Of course, the glow tube 8 is preferablyidisposed inan opening in the control panel of the set so `that the 70 vIt may be`desired to have ythe glow indicator 75 p tu'be Sfouly function as'anaudio-'coupling deviceA and` a .resonancelor tuning, indicator; InFig..f2*is. shown a modification of the detector andi audio. amplifiercircuits of Fig. 1 wherein the glow tube is. shown asof' an elongatedtype 8',

one..- electrode of the `tube 8" being connected to0 the detector anodeside-.of resistor I0, while the other electrode of tube 8.' isjconnected to ground, and through another path including condenser I8 tothe control grid of the audio tube 1. The biasv for the control gridiof. tube 1 is provided through. the series resistors I9 and 20, and thebias on the audio. tube v1 does not changev at any time.

In; the arrangementl shown inv Fig.. 2 the detector tube 511s again a`grids leak, detector., but in this; case when a signal. is tuned in the`glow tube 8. beg-instoglow. It functions as an audio coupilingy pathbetween the detector plate circuit and the input electrodes of the audioamplifier tube 1 In other words,` in thisA modification the tube 8' doesnot function asa back-ground noise suppresser by virtue of audio biascut-off control, but rather acts as a background' noise suppresserbecause it functions as the audio coupling path. The tube 8',r due toitselongated configuration, appears like a thermometer when disposed inthe control panel of the receiver, the increasing glow informing the setoperator of the resonance condition of the receiver.

In Fig. 3 is shown a modification of the arrangement shown in Fig. 2wherein the audio signal coupling between the detector plate circuit andthe audio amplifier 1 is accomplished through a coupling condenser 2 I,the tube 8 functioning, as in Fig. 1, as a control for the audioamplifier bias as well as a tuning indicator. The cut-off bias for theamplifier tube 1;in the absence of signal energy, is lapplied throughresistors Ri and R2. When signal energy is received, and the strikingvoltage of tube 8 exceeded, the negative bias on the control grid oftube 1 is decreased, and the audio amplifier rendered operative.

It will now be appreciated that in Fig. 1 the tube 8 and its associatedcircuits combines with the resonance indication function, the twoseparate functions shown in Figs. 2 and 3, to wit: audio bias controland audio signal coupling between detector plate circuit and audioamplifier network. It is also to be clearly understood that the presentinvention is not limited to a gas discharge device 8 which is filledwith neon gas, since any other gas filled tube could be employed inplace of a neon tube, and such gas fillings are too well known to beenumerated. Again, the detector and audio tubes 5 and I in each figuremay be of the well known duplex diode triode types. Also, theresistance-capacity coupling of Fig. 3 may be replaced by transformercoupling.

While I have indicated and described several systems for carrying myinvention into effect it will be apparent to one skilled in the art thatmy invention is by no means limited to the particular arrangements shownand described, but that many modifications may be made vwithoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

l. A radio receiver of the type including a detector and a succeedingaudio amplifier, characterized by the fact that a gas discharge deviceis connected between the detector plate circuit and the amplifier inputcircuit, and means connected in theamplifler 'inputcrcuit for biasing`the ampli-flier` to cut-oli" in the absence of signals, saidldischarge-device being of such construction thatit isl renderedconductive and glows when signals are impressed on the detector input,said device additionally being! connected between the detectora plateand amplifier grid for transferringv detected# signal energy to theaudio amplifier when conductive, and' said device being connectedto theamplifier grid in opposition to said rbiasing#-rrif'zzin'sfor removingsaid amplifier'cut-oif blaswhen the device becomes conductive. Y

k2. .In combination in a. radio receiver, a source of radio frequencyenergy, a detector, an audio amplifier, a gasdischarge tube connectedbetween the detector output circuit andthe amplifier input circuit, saiddischarge tube being in series between the detector plateand theamplifier grid and having a strikingr voltage characteristic such thatit becomes conductive when radio frequency energy above a predeterminedintensity level is impressed upon the detector, andthe connection fromthe tube to they amplifier grid being such that the effective voltagedifference between the amplifier grid and cathode is changed by the tubespace current new'.

3. In a receiver, as defined in claim 2, said tube being a neon tube,and being the sole coupling element between the detector and ampliiierwhereby it is adapted to transfer detected signal energy to said audioamplifier when it is rendered conductive, said neon tube additionallyindicating the resonance vcondition of the receiver.

4. In a radio receiver, las defined in claim 2, said audio amplifierincluding in its input circuit means for biasing the amplifier tocut-off `in the absence of signals in the detector input circuit, saiddischarge tube connection to the amplifier grid being in opposition tosaid biasing means for reducing the cut-off bias when the tube becomesconductive by virtue of said series connection.

5. In a radio receiver of the type including a detector and a followingaudio amplifier, a neon glow tube connected between the detector platecircuit and the audio amplifier grid circuit and comprising the solecoupling element therebetween, and means for normally maintaining thecontrol grid of the audio ampliiier negatively biased to cut-off, saidneon tube being connected to the amplifier grid in opposition to saidbias means and having a characteristic such that it becomes conductiveto decrease said cut-off bias, and operates to transfer detected signalenergy to said audio amplifier when signals above a predeterminedintensity level are impressed upon the detector.

6. In a radio receiver of the type including a 60 detector and afollowing audio amplifier, a condenser connected between the detectorplate circuit and the audio amplifier grid circuit, said condenser beingadapted to transfer detected signal energy to the audio amplifier, andmeans common to the detector plate circuit and the audio amplifier inputcircuit, including a gas discharge tube, for biasing the audio amplifierto cut-off in the absence of signal energy and decreasing the cut-offbias in the presence of signal energy. Y

'7. In a receiver of the type including a radio frequency ampliiier, adetector and an audio frequency'ampliiier, means for regulating the gainof the radio frequency amplifier in response to signal amplitudevariations, means in the audio amplifier input circuit for biasing theaudio am- Y plier to cut-olf in the absence of signal energy in thedetector input circuit, and a coupling path between the detector platecircuit and theaudio amplifier input circuit, said coupling path inftheinput electrodes of the rst tube, a gasV dis-y charge tube includingapair of electrodes connected between the plate of the rst tubeand thegrid of the second tube so that the. gas dis-Y charge path is in seriesbetween the said plate and grid, the potential diiference between theinput electrodes of the second tube being changed by the space currentof the gas tube when the latter is rendered conductive.

9. In a radio receiver including a detector, a neon glow tube in thedetector plate circuit, said glow tubehaving a voltage `characteristicsuchV that it becomes conductive and glows when sig., nal energy above apredetermined intensity level is impressed upon the detector inputcircuit, and an audio frequency amplifier having its control gridconnected to the detector plate through the electrodes of said glow tubein a circuit arrangement such that the potential difference between theamplifier input electrodes is changed by the glow tube space current. Y

10. vIn aisignalV transmission system, a pairV of cascaded tubes, asource of signals coupled to the input electrodes of the rst tube, a gasdischargetube including a pair of electrodes connected between the plateof the rst tube and the grid of the second tube so that the gasdischarge path is in series between the said plate and grid, thepotential difference between the input electrodes of the second tubebeing changed by the space current of the gas tube when the latter isrendered conductive, and means responsive to variations in signalamplitude at the source for automatically maintaining the signalamplitude at the input electrodes of the rst tube substantially uniform.I

{WINFIELD R. KOCH.

